Method and apparatus for magnetic separation of ores



Oct. 16, 1956 A, L. J. QUENEAU 2,766,883

METHOD-AND APPARATUS FUR MAGNETIC SEPARATION OF ORES Filed Oct. 20, 1954 4 Sheets-Sheet 1 a as was 2 1 I 1].) i{, .2 I

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E Q i INVENTOR 4=LE| AUGUST/N L. J. QUENEAU ATTORNEY Oct. 16, 1956 A. J. QUENEAU 2,766,888

METHOD AND APPARATUS FOR MAGNETIC SEPARATION OF ORES Filed Oct. 20. 1954 4 Sheets-Sheet 2 2o. 23 /a 0 m INVENTOR 34 AUGUST/N L. J QUENEAU ATTORNEY 3- 1956 A. L. J. QUENEAU 2,766,338

METHOD AND APPARATUS FOR MAGNETIC SEPARATiON OF ORES T 1: I. E

INVENTOR BY I ATTORNEY Oct. 16, 1956 V A, L. J. QUENEAU 2,766,883

METHOD AND APPARATUS FOR MAGNETIC SEPARATION OF ORES Filed Oct. 20, 1954 Y 4 Sheets-Sheet 4 INVENTOR AUGUST/N L'J QUENEAU ATTORNEY United States Patent NIETHOD AND APPARATUS FOR MAGNETIC SEPARATION OF ORES Augustin L. J. Queneau, Far Hills, N. J.

Application October 20, 1954, Serial No. 463,392

Claims. (Cl. 209-219) This invention relates to a method of and apparatus for separating magnetically susceptible mineral values from ores, residues and like materials containing constituents which are undesirable or which interfere with smelting of the materials to recover the metal content. While the invention is especially applicable to the treatment of iron ores, it has other valuable applications.

As is well known, large bodies of iron ores in the form of hematite, limonite and the like are available, in which iron oxide is mixed with such quantities of silica, silicates and other gangue materials as to make the direct smelting of such ores in a blast furnace uneconomical. Owing to the rapid exhaustion of the known beds of high grade iron ores, the iron and steel industry will in the near future be required to depend more and more on the available lower grade ores. This necessitates the provision of economical means for separating the values from the gangue materials. This is not easy to accomplish in view of the relatively low magnetic susceptibility of the metallic values in some ores. Hematite, for example, has a very low magnetic susceptibility, and it cannot be separated magnetically by conventional dry magnetic separators.

In U. S. Patent No. 2,088,364 of myself and Edwin E. Ellis and in my U. S. Patents Nos. 2,154,010, 2,258,194 and 2,290,892, there are disclosed certain methods and apparatus whereby the separation of mineral values of relatively low magnetic susceptibility from low grade ores can be accomplished. In the use of the apparatus disclosed in the aforesaid patents the ore, in the form of a pulp with water, is caused to flow under a constant hydrostatic head past rotating poles which attract and divert the magnetically susceptible material from the path of flow of the pulp and thus deliver valuable portions of the ore into containers separate from the g-angue materials. In Patent No. 2,258,194, I have described a duplex separator in which the flowing material is subjected to the action of two concentrated magnetic fields successively to effect a more complete separation of values from the gangue.

The separators of the previously mentioned patents have been found particularly useful with ores containing mineral values of relatively low magnetic susceptibility such as hematite. However, I have found when treating mixed ores e. g., ores containing, besides hematite or another mineral value of low magnetic susceptibility, even relatively low'proportions of materials having a high magnetic susceptibility such as magnetite, the magnetite must first be removed by subjecting the pulp to a 'low intensity separation. Otherwise, it will cause bridging across the rotating poles of the separator and prevent the flow of pulp therethrough. This entails two separate and successive operations in the same apparatus or two difierent separators.

It is an object of the present invention to provide improvements in methods and apparatus for separating mineral values from ore pulps in which values of high magnetic susceptibility, such as magnetite, as Well as those 2,766,888 Patented Oct. 16, 1956 ice 2 of lower magnetic susceptibility, .such as hematite, limonite, goethite and the like, may also be separated and recovered in a single operation.

A further object of the invention is the provision of a multiple separator in which the material is subjected successively to a plurality of magnetic fields of increasing intensity, so that separation is obtained without incurring the cost incident to the use of a number of independent separators.

Another object of the invention is the provision of a separator capable of delivering concentrates and middlings as well as tailings including the gangue material.

A further object of the invention is the provision of means for varying the strength of the magnetic fields, increasing them progressively as the pulp passes through the separator.

It is the primary object of the invention to provide a method of and apparatus for separating the mineral values from ores in an economical and commercially practicable manner.

Other objects and advantages of the invention will be made apparent by reference to the following specification and the accompanying drawings, in which:

Fig. 1 is a plan view of a separator adapted to accomplish the purpose of the invention;

Fig. 2 is a vertical section on the line 22 of Fig. 1;

Fig. 3 is a vertical partly diagrammatic side elevation on the line 33 of Fig. 1;

Fig. 4 is a part vertical section and part side elevation on the line 44 of Fig. 1;

Fig. 5 is a plan view of the bottom of the separator;

Fig. 6 is a section on the line 6-6 of Fig. 4;

Fig. 7 is a section on the line 7-7 of Fig. 4;

Fig. 8 is an elevation of the face of one of the polar extensions with the rotating poles and the covers therefor removed;

Fig. 9 is a sectional view illustrating an arrangement of the rotating poles of modified form that is adapted to avoid bridging of material of high magnetic susceptibility;

Fig. 10 is a sectional view of a rotating pole similar to those shown in Fig. 9, but of modified construction;

Fig. 11 is a sectional view illustrating a separator provided with rotors carrying permanent magnets;

Fig. 12 is a part side view of one of the separator rotors of Fig. 11 with one of the end plates removed;

Fig. 13 is a part end elevation and part section taken on the line 13-13 of Fig. 12;

Fig. 14 is a view similar to Fig. 2 illustrating a modified form of the separator; and

Fig. 15 is a section on the line 1515 of Fig. 14.

According to the presently preferred form of apparatus for practicing the invention, a magnetic field is estab lished across the path of flow of the ore pulp between a pair of opposed rotating pole members by the provision of cores which are suitably wound with a multiplicity of coils of wire adapted to be supplied from any suitable source of direct current. The cores are connected by a yoke to complete the electromagnetic circuit except for the gap between the cores. Preferably, in order to permit modification of the magnetic intensity at different levels of the separator at least two such yokes, with corresponding cores and coils, are employed. By varying the number of turns of wire on the cores, the desired differences in the intensity of the magnetic fields can be obtained. Polar extensions are advantageously connected to the cores to afiord a relatively long vertical gap and extend the high intensity zones lengthwise of the path of the descending pulp. Between the extensions, a separator box is disposed, through which the pulp flows. The pulp is supplied at the top. The bottom outlet of the separator box has a restricted opening, and

masses clockwise direction.

In accordance with the present invention, the rotating pole members, at least in the upper levels of the separator, do not present points or zones of high magnetic flux concentration more or less uniformly distributed throughouttheperipheral surfaces thereof as has heretoforebeen customary in the" magnetic separators constructed according to the teachings of the patent hereinbefore mentioned. Cut-out portions are formed at equispaced distances around the periphery of the rotating pole member, these cut-out portions being separated by radially extending arms of high magnetic permeability which terminate in arcuate surfaces corresponding to the maximum diameter of the pole member. Thesearcua-te surfaces carry teeth which serve to define points or zones of relatively high magnetic flux concentration in a similar manner as in the types of rotating pole members described in the prior patents hereinbefore mentioned. The thus modified rotating pole members are so associated within the recesses on the opposite sides of the flow" path forthe pulp through the separator that they rotate out of phase, that is to say, the portions thereof having such arcuate surfaces are brought into positions opposite the cut-out spaces in the corresponding but opposite pole member'as the pole members rotate. Thus the concentration of the magnetic flux increases to a maximum at one side of the flow path as one of the arcua'te surface portions is brought into close proximity to the path of flow of'the pulp through the separator while simultaneously decreasing to a minimum at the opposite side of the flow path adjacent the cut-out portion in the opposite pole member.

It will be seen that there is an important alternation of the field intensity at the opposite sides of the path of flow of the ore pulp betweenthe two rotating'poles in and. adjacent the horizontal plane passing through the axes of the poles. Thischange in the field intensity, or the magnetic flux concentration, is directly proportional to the increase and decrease of the distance between said path and the outward ends of the arms which carry such arcuate surface portions, this change in field strength being expressed in accordance with the equation .4arNI netic susceptibility than that of the body of the rotating pole. Thus, for example, the rotating pole may be made from sheets of low metalloid steel alternating with sheets of zinc in the preferred form of the invention, with recesses as previouslydescribed. The recesses may, how ver, 'befilled; with grey iron inserts. Grey'f cast' iron, graphitic iron, has a magnetic susceptibility some what less than half. that of low'metalloid steel.

The particles of'values separated at each o' f the upp 'steel and of zinc.

levels of the separator may be directed by sloping walls toward and into downwardly extending passages or compartments at one side of the separator box and are thus removed. The particles deflected by the lowermost set of rotating poles are separated similarly and are withdrawn through a separate outlet, while the gangue which remains in thepulp is withdrawn at the bottom through a restricted outlet adapted to permit limited flow so that the hydrostatic headis maintained in the separator box.

:Thus, it is possible to secure concentrates, middlings and tailings from the separator. The tailings are delivered substantially 'free from values and consist of the gangue materials in the pulp. The middlings are separately collected and usually will be retreated. During the passage of the material-through the separating path, it is subject continuously to a magnetic field which varies in intensity with the distance from the rotating pole members; hence the susceptible particles do not lose polarity. This materially assists the deflection of the;

susceptible particles as'they enter the successive more.

highly concentrated or intense fields. It is desirable to vary the magnetic flux at different levels so that the most susceptible particles are first defiected. This is accomplished in the manner hereinhefore indicated by employing rotating poles having recesses or poles with the recesses filled with material of lower magnetic susceptibility than the material forming the poles at the lower end of the separator.

Thus, in the uppermost set of rotors, which treat the incoming fresh ore pulp containing a higher proportion of magnetite, the rotors are preferably deeply recessed.

They are also preferably of laminated construction, the laminations consisting of alternate sheets of low metalloid The thickness of the sheets may be, for example, .075 inch. The second set of rotors, for treating pulp with a lower proportion of magnetite, are also preferably of the deeply recessed type and laminated, as in the first set. The third set of rotors, for treating a residue. from the previous separations containing, for example, little or'no magnetite but containing a large pro portion of the hematite values along with the gangue particles, should be of the deeply recessed type but of 7 solid steeL- The fourth and last pair of rotors, for treating an ore pulp containing almost exclusively hematiteor the like and the gangue residues, should be cylindrical,

with teeth on the surface and made of solid low metalloid steel. Of course, the foregoing is subject to variation,

being merely illustrative of the preferred embodiment of the invention. 7

Referring more particularly to the drawings, 5 indicates a separator box which is supported in any suitable manner. Inlet pipes 6 are provided through which to introduce the pulp. These pipes have openings 7 below the upper surface of the pulp. The pulp level is maintained constant by means of a weir 8 connected to an outlet pipe 9. At the bottom of the separator box, outlet pipes 10 are provided. Flow of pulp through the outlet pipes is controlled by means of diaphragms 11 eachhaving an opening 12. of restricted size. By suitably selecting the diaphragms according to the size of the opening 12 the flow of pulp through the separator box is so regulated as to maintain a constant hydrostatic head in the flowing pulp.

The sides of the separator box, as shown in Fig. 4, are provided with a plurality of arcuate recesses 13 on each side thereof; In these recesses, rotating poles 'li, 15, 17 and'18 are mounted on shafts 19, 20, 21 and 22, which are suitably journaled in frame members 23 and 2.4 The shafts 19 are driven from any suitable'source of power, not shown, and the shafts 20, 21 and 22 are driven from the shafts 19 through the intermediary of suitable gearing. As shown in Fig. 3, the gears 25 and 26 mounted on the shafts 19 drive the successive pairs 1 of gears 29 connected respectively to the shafts 20, 2 1 and inopposite directions, clockwise on one side and counterclockwise on the other, as shown in Fig. 9.

Beneath each of the arcua'ze recessss 13, upwardly directed partitions 30 and 31 are provided with their edges spaced from the wall of the separator box so that, as the particles of magnetically susceptible material are drawn laterally toward the inner sides of the side wall portions of the separator box defining the arcuate recesses and then outwardly along the lower sides of the walls of these recesses, they are directed behind the partitions 30. The more magnetically susceptible material continues to travel laterally along the undersides of said walls and passes behind the partitions 31, thus not only separating the magnetically susceptible particles from the pulp passing downwardly through the separator box, but also effecting a further separation into concentrates and middlings. The main body of the pulp continues to flow downwardly into the zone of the next succeeding rotating poles which similarly separate additional magnetically susceptible particles from the pulp. When third and fourth sets of rotating poles are provided, as shown in Fig. 4, and each succeeding set is more strongly energized so as more strongly to attract the mineral values of lesser magnetic susceptibility, such as hematite, limonite and the like, additional separations of such magnetically susceptible particles will take place as the pulp passes the third and fourth sets of poles.

The magnetically susceptible particles separated by the three upper sets of rotating poles are diverted by transversely inclined partitions 32 as shown in Fig. 2, into a downwardly extending pipe 33. The partitions 32 are shown as disposed at an angle of 45 but this angle, of course, may be modified according to operating conditions. The magnetically susceptible particles which are withdrawn into the pipe 33 pass downwardly through the pipe and escape through an outlet 34 as the high grade concentrate. The pulp that remains after passing the poles 17 is finally passed between the rotating poles 18 which draw the remaining magnetically susceptible particles laterally outwardly and past a partition 35. These particles pass into an outlet 36 and consist of a lower grade of concentrate which may be returned for retreatment as part of the feed or otherwise utilized. The residual gangue materials in the pulp are then withdrawn as previously described through the outlet pipe 10. The middlings collected in the compartments defined between the respective partitions 39 and 31 may be withdrawn from these compartments in a similar manner as the concentrates and then retreated in the same or a succeeding separator unit to recover a concentrate therefrom.

In order to supply the magnetic flux, cores 37 are connected to a yoke 38 and carry coils 39 which are connected to a suitable source of direct current. The magnetic circuit is closed through the yoke 38 except for the gaps between polar extensions 40 which are secured to the cores 37. The polar extensions 40 extend upwardly along the edges of the separator box 5 and are provided with a plurality of arcuate recesses 41 in which the several rotating poles operate. As already indicated, twin sets of .cores 37, yokes 38 and coils 39 may be provided and connected to separate sources of power, the windings of the coils being varied so that the uppermost set affords a lower magnetic flux than the lower sets. The faces of the polar extensions 40 adjacent the sides of the separator box 5 are grooved to provide a plurality of projections 42. The projections 42 aiford a plurality of relatively concentrated magnetic fields extending through the path of travel of the pulp as it descends in the separator box. These concentrated fields have the efiect of diverting the magnetically susceptible particles toward the sides of the separator box so that they pass readily into the zones of maximum magnetic intensity provided by the rotating poles 14 to 17 inclusive. Consequently, the separating efficiency of the rotating poles is increased.

Referring particularly to Fig. 9, the form of the rotating poles, particularly at the upper zones of the separator, will be readily understood. The poles 14, for example,

6 are secured to shafts 19. As previously indicated, the poles 14 are formed of laminations consisting of alternate sheets of low metalloid steel and of zinc, the thickness of the sheets being usually .075 inch. The poles are formed with recesses 43, thereby providing projecting arms 44 having teeth 45 at the periphery thereof. As shown in Fig. 9, the opposed rotating poles 14 are out of phase, so that one of the arms 44 projects toward the corresponding recess 43 in the opposite rotating pole. Thus as the poles rotate, there is a continuous variation in the flux concentration between a maximum and a minimum, and it has been found that the use of poles of this particular type when mounted for rotation in out of phase relation as shown will permit the separation of particles of high magnetic susceptibility such as magnetite from a m xed ore pulp without danger of bridging, even though as much as 2% of magnetite may be present in the ore undergoing treatment.

When the poles 14 are in the angular positions shown in Fig. 9, with one of the pole arms 44 horizontal, the field intensity in the narrowest portion of the separator box is at its maximum value. The field intensity is greatest near that horizontal pole arm, the flux being more widely spread on the opposite side of the narrow portion of the separator box. As the poles continue to rotate, when they have passed through an angle of approximately 30 from the position shown, the lower portion of one of the recesses 43 of the left hand pole will be directly opposite the upper portion of one of the recesses 43 of the right hand pole. The air gap in the magnetic circuit which extends across the throat of the separator box is then at a maximum and the field intensity in the throat is therefore at a minimum. After the poles have rotated another 30, one of the arms 44 on the right hand pole will have moved to a horizontal position, and will be opposite the center of one of the recesses 43 of the left hand pole. The field intensity in the throat of the separator box is again at a maximum, but this time the field intensity is greatest along the right hand side of the throat, the flux being more widely spread along the left hand side.

The pole arms 44 and the recesses 43 are so proportioned that the minimum field intensity is insufficient to maintain in the throat of the separator box any bridge of magnetic particles which may form there. Consequently, any such bridge which tends to form there during an interval of maximum field intensity will fall during the next interval of minimum field intensity. Also, since the field intensity is never at its maximum on both sides of the separator box at the same time, the downward sweep of the flux on the side which is at its maximum field intensity will tend to carry downward one side of any bridge which tends to form there. By having the field intensity at its maximum on only one side at a time, the formation of bridges is effectively prevented.

The teeth 45 in the ends of the arms 44 function in the same manner as in the prior art structures toprovide small local Zones of alternate increased and decreased field intensity, which zones rotate with the poles and urge the attracted magnetic particles to move along the inside surface of the curved wall of the separator box toward the sides of the box.

It will be observed that the portions of the separator box wherein the field intensity is decreased by the action of the recesses 43 are much greater in size than the small local zones Where the field intensity is decreased by the gaps between the teeth 45. Furthermore, the reduction in the field intensity produced by the recesses 43 is far greater than the reduction produced by the gaps between the teeth 45.

The reduction of the field intensity at the recesses 43 must be great enough so that the remaining field is unable to maintain any bridge of magnetic particles or a portion thereof against the combined action of gravity "7 and of the downwardly moving high intensity field on the Opposite side of the separator box.

The next set of rotating poles 15 is preferably con: sttucted of laminations of low metalloid steel and zinc, the thickness of the sheets of each metal being .075", but without the provision of the large recesses 43 shown in the poles 14. Instead, the entire area of the cylindrical pole members will be provided with teeth 45.

The rotating poles 17 of the third set are preferably constructed similarly of laminations of low metalloid steel and Zinc, t'ne former being .075 inch thick and the latter .050 inch thick, thus providing a greater crosssection of the ferrous metal for the magnetic flux than in the first pair of rotating poles. The rotating poles 18 of the fourth set are preferably made of solid low metalloid steel and of full cylindrical section with teeth on the periphery.

Referring to Fig. 10, a modification of the rotating poles as compared to those shown in Fig. 9 is illustrated.

'The poles :6 are secured to the shaft as in the preceding embodiment of the invention and are provided with arms 47 forming recesses 43. The latter are filled with plugs 49 of a material of diiferent magnetic susceptibility, for example grey cast iron, the plugs being held by bolts 50. Thus the rotatable pole 46 may be constructed of laminated sheets of low metalloid steel and zinc as in the structure" shown in Fig. 9, with plugs of grey cast iron or the like. Also, it will be noted that whereas three arms are shown in Fig. 9, any desired number of such arms may be employed, as for example five in Fig. 10. It will be further understood that the thickness of the laminations as set forth is merely illustrative of the preferred embodiment of the invention.

In the structure of Fig. 10, the plugs 49 and the arms 47 have substantially the same peripheral extent. This is to be contrasted with the arrangement of Fig. 9, wherein the arms 44 have substantially one-third of the peripheral extent of the recesses 43. When the modified pole structure of Fig. is used, the poles on the opposite sides of the separator box are positioned out of phase in the same manner as they are in Fig. 9, so that each pole 47 on one side comes opposite a plug 49 on the. other side. In this manner, the maximum field intensity is shifted back and forth from one side to the other'in the separator box in the same manner as in Fig. 9. The difference between the maximum and minimum field intensity in Fig. 10 is not as great as in Fig. 9, since. the difference between the maximum and minimum reluctance of the magnetic circuit is not as great. Also, there is no time when the field intensity is reduced substantially across the entire separator box as there is in the structure of Fig. 9 when portions of two recesses 43 are opposite each other.

As hereinbefore indicated, 'it is desirable to vary the magnetic flux at various levels of the separator so that the effective flux increases asthe pulp flows downwardly through the separator. This is accomplished primarily "by variation in the configuration and structure of the rotating poles so that material ofhi-gh magnetic su s. cepti'bility such as magnetite is separated without bridging at the top of the separator and other constituent values of the pulp are subjected progressively to increasing intensity of the magnetix flux as the pulp flows downwardly, by the use of rotatable poles of modified form and structure. Magnetite, for example, may have a magnetic suscepti-bility of. 300 to 350, whereas hematite, goethite, siderite, etc. may have susceptibilities of 30 or even less down to 8 and possibly lower. By using rotating poles, as shown for example in Fig. 9, at the top of the separator, most of the magnetite is immediately separated and withdrawn, the magnetic flux at this level of the separator being relatively weak but suflicient,

nevertheless, to draw the magnetite from the stream of a mesa-st r sq sr-ti ilit than ma n ite and. b m dif in the rotating poles'at the 'lower end of the separator, the magnetic flux may be increased progressively. Furthermore, as already indicated, the value of the flux may be modified at difierent levels of the separator by the use of twin sets of poles having windings of different value.

Instead of using the sloping partitions 32 shown in Fig. 2 for directing the concentrates collecting in the concentrates compartments to the common discharge pipe 33,, I may utilize, as shown in Figs. 14 and 15 a partition secured on one side to the side of the separator box and having a free edge spaced from the wall of the sepaa rator box and forming a trough in which a screw conveyor '52 is supported on'a shaft 53 and driven from any suitable source of power to feed the separated material into a pipe 54 which discharges the concentrate at the bottom of the separator in the manner previously deconcentration of magnetic flux at the desired points for a the current consumed. The shafts upon which the ro-j tat-able. poles are mounted should be made of stainless steel or other non-magnetic material of suitable strength towithstand the powerful force of the magnetic field which tends to. distort the shafts. The separator box 5 and its appurtenant parts must be made of non-magnetic material such as brass, aluminum and the like, in order that the magnetic flux may function properly to draw the magnetically susceptible particles into the desired channels and thus separate them from the pulp;

As in the case of the separator described in my earlier Patent No. 2,290,892, it is necessary to provide outlets for the separated materials which will insure the maintenance of the desired height of liquid in the separator box. I may employ, in connection with the outlets 34 and '36, the means disclosed in Fig. 2 of Patent No. 2,290,892 or any other similar means adapted to accomplish the function. As the particles of magnetically susceptible material are withdrawn from the main downward how of the pulp, they displace water in equal volume present in the concentrates and middlings compartments, causing a current of water to how outwardly past the edges of the partitions 30 and '31 into the downwardly moving pulp stream, thus tending to'prev'entthe entrance of non-magnetic particles into the stream of concentrates which are continuously separated from the pulp stream. Although the invention has been described with particular reference to its embodiment in an apparatus wherein the magnetic field is created by the use of electromagnets, it is to be understood that the principles involved 7 are applicable when using permanent magnets, There is shown in Fig. 1'1 an embodiment of apparatus wherein a pair of rotors carrying permanent magnets are disposed at the. opposite sides of a separator box which may be generally similar in shape and construction as that hereinbeforedescribed and wherein like reference numbers have been applied to similar parts.

As shown more particularly in Fig. 11, a plurality of setsof permanent magnets are arranged at spaced intervals about the periphery of a pair of rotors 58 mounted on shafts '59 and disposed within recesses 13 on opposite sides of a separator box '5. The rotors are so mounted and connected to appropriate driving means,- not shown, that the magnets of one of the rotors will be brought into. close proximity 'to the throat section of the separator box between the rotors in out of phase re- 7 lation to the magnets on the opposed rotor. Each mag-.

net set or section is shown as made up of two horseshoe magnets, and it will be understood that the number may bev-aried according to the size of the rotor or for other reasons;

As shown more particularly in Fig. 12, the individual magnets. of each set are secured by bolts 61 to two circugreases 9 lar steel bars 62 which in turn are secured by bolts 63 to the sides of a pair of spaced disks 64 made of a nonmagnetic material such as aluminum. The circular disks are supported in spaced relation on the shaft 59 and are held in the desired spaced relation by a spacing ring 55 concentrically arranged on the shaft 59 and by the magnets 60 each of which has the leg thereof which terminates in the north pole secured to one of the bars 62 and the opposite leg terminating in the south pole secured to the opposite bar 62. Owing to the arrangement of the magnets of each set with the like poles on the same side of the rotor, there is no tendency for lines of force to be established between the adjacent magnets on the same side of the rotor. Instead the elfective magnetic field is established across the gap between the north and south poles of each individual magnet. The effectiveness of the magnetic field is increased by the arrangement by which the individual magnets are bolted to the two circular bars 62. This serves to shorten the magnetic gaps between the poles of the individual magnets, thus increasing materially the effective strength of the magnets and the penetrating power thereof.

The peripheral surfaces of the circular bars 62, throughout the portion of the arcuate extensions thereof that corresponds to the extent of each set of magnets when measured circumferentially of the rotor, are provided with incised islets or rectangles separated by grooves extending both circumferentially and crosswise of the bars, thus concentrating the magnetic flux in relatively small pencils issuing in the main along the sharp edges and especially at the corners.

Preferably the rotors are of enlarged diameter as compared to the rotors that are employed in the electromagnetic type of separator. A suitable dimensioning of the rotors and of the incised islets and the intervening grooves that are provided on the peripheral surfaces of the bars is that disclosed in my copending application Serial No. 463,393 filed October 20, 1954, wherein I have disclosed a separator equipped with permanent magnets similar to those shown in Figs. 12 and 13 hereof except that the rotors are provided with a continuous series of magnets throughout the peripheries thereof.

For example, the rotor of the present invention may have a diameter of 18 /2" and the two circular steel bars may have a cross-section of 1 /3" x 1%" when using mag-nets having a contact pull of 100 pounds. The peripheral surfaces of the bars 62 in that portion of the arcuate extent thereof which is opposite the two magnets of a given set is provided with parallelly spaced grooves 65 each /2" in depth and /s" wide and extending crosswise to the circumferential extent of the bars. As shown these grooves are spaced apart along the peripheral surface. A second series of grooves 66 having a depth of i and a width of and spaced apart are formed lengthwise of the bars thereby cutting the surfaces into islets 3 X As previously indicated, the magnetic flux established with the use of permanent magnets is most intense between the north and south poles of the individual magnets carried by a given rotor and, therefore the conditions under which bridging may arise are dilferent from those which exist when an electromagnetic separation is being employed. Since the flow path between the north and south poles of the individual magnets is generally parallel to the axes of the" rotors and strongest at the side of the throat portion of the separator box closest to the permanent magnets, the separating action is afiected only slightly, if at all, by the presence of an opposed rotor since the effective separation is determined primarily by the strength of the magnets carried by a given rotor and the distance between the path of rotation of the poles of the magnets and the flow path of the pulp. In other words, the capacity of the separator is determined by the extent to which an eifective magnetic field can be established from one side of the flow path inwardly into that flow path. Consequently, when using a single rotor the width of the flow path for the pulp will be determined according to the strength of the field that may be developed between permanent magnets carried by a single rotor disposed as closely as practicable to one side of that path. However, when dealing with ores containing a relatively high proportion of a mineral having a high magnetic susceptibility such as magnetite, it may be desirable to increase the capacity of the separator by providing rotors carrying permanent magnets at both sides of the separator box so as to act upon the downwardly flowing pulp at both sides and thereby increase the output while at the same time providing a wider throat section or gap between the rotors. Not only will this resultin doubling the capacity of the separator when using magnets of a given strength and dispositionybut also will tend to minimize the tendency to blocking or bridging that might arise with a throat section ofthe smaller dimension required when using a single rotor. Nevertheless, even when the capacity is doubled in'this manner conditions may arise, especially when the ore carries a higher proportion of magnetite, where there would be a tendency to bridging of the gap or throat section of the separator due to the attraction of the magnetite to the walls of the box in the throat section. This tendency is avoided by mounting the permanent magnet rotors in the out of phase relation above described.

The method and apparatus as described insures the maximum efiective separation of the values from the ores with the minimum of equipment and power consumption. It is applicable particularly to ores consisting of mixtures of magnetite and hematite and the like. By subjecting the pulp successively to a magnetic flux of progressively increasing intensity, in the manner described with reference to the preferred modification, substantially all of the values are removed by the elfect of the three upper sets of rotating poles. Any remaining values are separated by the lowermost set of rotating poles, and the gangue is delivered substantially free from values.

Various changes may be made in the details of the procedure and in the apparatus as described without departing from the invention or sacrificing the advantages thereof.

This application is a continuation-in-part of Serial No. 179,458, filed August 15, 1950, and now abandoned.

I claim:

1. The improvement in the wet magnetic separation of materials consisting of mixtures of magnetically susceptible materials varying substantially in their magnetic susceptibilities such as mixtures of magnetite and hematite, which comprises flowing a suspension of a mixture of said materials in a liquid medium under a contr olled hydrostatic head downwardly in a restricted path through a generally horizontally extending magnetic field and thereby causing magnetically susceptible particles to be attracted to the sides of said path, alternately increasing and decreasing the intensity of the field at the opposite sides of said path out of phase, and, during the intervals of increased field intensity, magnetically urging said particles collected at the side then subjected to the increased field intensity downwardly and laterally away from said restricted path to points of collection separated from the main downward flow of the residue of said suspension.

2. The improvement in the wet magnetic separation of magnetically susceptible particles from a pulp containing magnetite mixed with iron ore particles of lower magnetic susceptibility, non-magnetic particles and water, which comprises flowing a suspension of a mixture of said materials in a liquid medium under a controlled hydrostatic head downwardly in a restricted path through a generally horizontally extending magnetic field, and there-- by causing magnetically susceptible particles to be at tracted to the sides of said path, alternately increasing and decreasing the intensity of the field at the opposite sides of saidpath out of phase, and, during the intervals of increased field intensity, magnetically urging said part.i--

cles collected at the side then subjected to the increased field intensity downwardly and laterally away from said restricted path to points of collection separated from the main downwardly flow of residue of said suspension, and repeating all said steps on the residue of said pulp under conditions of increased maximum field intensity.

3. The improvement in the wet magnetic separation of magnetically susceptible particles from a pulp containing magnetite mixed with iron ore particles of lower magnetic susceptibility, non-magnetic particles and water, which comprises 'fiowing a suspension of a mixture or" said materials in a liquid medium under a controlled hydrostatic head downwardly in a restricted path through a generally horizontally extending magnetic field and thereby causing the more magnetically susceptible particles to be attracted to the sides of said path, alternately increasing and decreasing the intensity of the field at the opposite sides of said path out of phase, and, during the intervals of increased field intensity, magnetically urging said particles collected at the side then subjected to the increased field intensity downwardly and laterally away from said restricted path to points of collection separated from the main downward flow of the residue of said suspension,

' thereafter passing the residue of said pulp under a controlled hydrostatic head downwardly in a restricted path through a magnetic field of sufiiciently increased intensity to attract the iron ore particles of lower magnetic susceptibility to the sides of said path and recovering said particles separately from the remaining residue of the pulp. I

'4. in an apparatus for the wet magnetic separation of materials consisting of mixtures of magnetically suscepti ble materials varying substantially in their'magnetic sus ceptibilities such as mixtures of magnetite and hematite, a vertically extending separator box provided with enclosing sides and bottom'walls for receiving and maintaining a liquid suspension of such material under a controlled hydrostatic head, means defining a restricted discharge opera ing in the bottom portion of said box through which to maintain a controlled discharge of a residue of said liquid suspension, said box having opposite sidewall portions provided with opposed inwardly extending arcuate 'recesses defining between them a narrow throat, rotors disposed within said recesses and cooperating to maintain a magnetic field throughout the extent of said throat, vmeans for alternately increasing and decreasing the intensity of the field at the opposite sides of said throat, means for urging magnetic particles attracted to the opposite sides or" said throat downwardly and laterally away from the main flow of the downwardly flowing liquid suspension, and means providing separate discharge passages for theattracted particles that are moved laterally away from said throat.

' 5. ln an apparatus for the wet electromagnetic separation of materials consisting of mixtures of magnetically susceptible materials varyings'ubstantially in their magnetic susceptibilities such as mixtures of magnetite and hematite, a vertically extending separator box provided with enclosing sides and bottom walls for receiving and maintaininga liquid suspension of such material under a controlled hydrostatic head, means defining a restricted discharge opening in the bottom portion of said box through which to maintain a controlled discharge ofa residue of said liquid suspension, said box. having opposite side wall portions provided withv opposed inwardly extending arcuate recesses defining between them a narrow throat, magnetic pole pieces disposed within sai recesses and cooperating to maintain a magnetic. field throughout the extent of said throat, means for alternately increasing and decreasing the intensity of the field atthe opposite sides of said throat, means for urging magnetic particles attracted to the opposite sides: of said throat downwardly and laterally away from themain flow of the downwardly flowing liquid suspension and means ill providing separate discharge passages for the attracted" particles that are moved laterally away from said throat.

6. In an apparatus for the wet electromagnetic separation of materialsconsisting of mixtures of'magnetically susceptible materials varying substantially in their magnetic susceptibilitiessuch as mixtures of magnetite and hematite, a vertically extending separator box provided with enclosing side and bottom walls for receiving and maintaining a liquid suspension of such material under a controlled hydrostatic head, means defining a restricted discharge opening in the bottom portion thereof through which to maintain a controlled discharge of residue of said liquid suspension, said box having opposite side Wall portions provided with opposed inwardly extending arcuc ate recesses defining between them a narrow throat, an eleetromagnet including rotatable pole pieces disposed within'said opposed recesses and cooperating to maintain.

a magnetic field throughout the expanse of said throat, said rotatable poles including a plurality of radial arms of high permeability separated by recesses of comparatively low permeability, said poles being positioned out'of phase so that as they rotate the arms on one pole'pass through the horizontal plane common to the pole axes simultaneously with the recesses on the other pole, said pole arms being effective to urge magnetic particles attracted to the sides of the box along said sides laterally away from said throat, and means providing separate discharge passages for the attracted particles that are moved laterally away from said throat.

7. In an apparatus for the wet electromagnetic separation of magnetically susceptible particles from mixtures of said particles with non-magnetic particles in which rotatable pole pieces are disposed in opposed relationon' opposite sides of a separator box through 'which a liquid pulp of said particles is passed during the separating oper ation, the improvement which comprises the provision of opposed rotatable pole pieces each including a plurality of radial arms of high permeability separated by recesses of comparatively lowpermeability, said pole pieces being mounted with their respective radial arms out of phase so that as they rotate the arms on one pole pass through the plane common to the pole axes simultaneously with the recesses on the other pole.

8. Apparatus for separating magnetic particles as defined in claim 7, in which-the recesses separating said ing separator box provided with enclosing side and bot tom walls for receiving and maintaining a liquid suspension of such material under a controlled hydrostatic head,

means defining a restricted discharge opening in the bottom portion thereof through which to maintain a controlled discharge of residueof said liquid suspension, said box having opposed side'wall portions provided with opposed inwardly extending arcuate recesses defining' between them a narrow throat, rotors disposed within said recesses and each carrying a plurality of permanent magnets each presenting the north and south poles thereof at the peripheries of said rotors with said poles aligned in planes passing through the axes of said rotors, whereby said individual magnets define magnetic fields which ex.- tend inwardly of the side walls of said box into said throat section from the opposite sides thereof when the respective magnets are brought into proximity to the walls defining said recesses, said magnets being spaced circumferentially of 'saidrotorsso as to define a plurality of magnetic fields separated by zones of susbtantially decreased magnetic intensity and said magnets on theone rotor. being positioned out of phase with respect to the magnets on 13 14 the other rotor so that as the rotors are turned the mag- 1,930,108 Recder Oct. 10, 1933 nets on the one rotor pass the plane common to the rotor 1,965,441 Tyden July 3, 1934 axes simultaneously with the zones of decreased magnetic 2,078,513 Stearns Apr. 27, 1937 intensity on the other rotor. 2,156,125 Payne Apr. 25, 1939 5 2,258,194 Queneau Oct. 7, 1941 References Cited in the file of this patent UNITED STATES PATENTS 910,664 Green Jan. 26, 1909 

